Process of manufacturing mercaptans



Sept. 3, 19,35. w. N. DAvls ET AL 2,013,203

` PRooEss oF MANUFACTURING MERCAPT'ANS Filed April 11, 1932 v 77mm new S r/z. L.

W4 TER Patented Sept. 3, .1935

UNITED; STATES PATENT OFFICE.-

Y 'Y 2,013,203 i carni-Ns N. Davis and Melvin M. Holm, Berkeley, Calif., assignors to Standard Oil Company oi California, San Francisco, a corporation Application April-11, 1932, serai No. 604,540

' comms. (ci. zoo-15s) This invention relates to a process of treating hydrocarbon-vapors or light petroleum distillates, for the purpose of producingmercaptans and mercaptides therefrom.

5 An object of this invention is to disclose and provide a method of preparing mercaptans from petroleum vapors .br distillates in a ready 'and economical' manner.

Another object iis to disclose' and provide a l method of treating petroleum vapors or distillates whereby said petroleum vapors or distillates are purified and simultaneously mercaptides an mercaptans are produced asa product.

A still further object of this invention' is to l disclose a particular sequence'of steps and conditions by means of which mercaptans may 'be readily produced from petroleum vapors or distillates.

Mercaptans are 'organic chemical compounds similar in type to alcohols but containing sulfur in place of oxygen. They are also known as thioalcohols or thiols. Mercaptans may be either aliphatic or aromatic, ethyl mercaptan, C2H5.SH, being a. typicalaliphatic thiol.

Although as stated hereinabove, the primary object of this invention is to disclosea process of obtaining 'mercaptans and mercaptides in suitable form for use as crude chemical reagents, odorants, etc., the p rocess of this invention Vis also applicable tothe purification of petroleum distillates and -petroleum vapors containing mercaptans. The products produced in accordance with this invention, namely, the various mercaptans, have a numberof 'various uses. Ethyl mercaptan, for example, is used in. the

production of products such as sulfonal, trional and tetronal. Other mercaptans, or mixtures thereof, may be used as odorants or signalling 'substances in fuel and illuminating gas. 40 Brieiiy stated, the ,processv of this invention comprises contacting a petroleum vapor or distillate with an alkaline solution at atmospheric or superatmospheric temperature, and then converting to mercaptans the mercaptides produced removed and separated by distillation and 'conden'sation or by acidiiying the mercaptide solution so as to liberate the mercaptans as a water- `immiscible oil. The process in its several modiiications will be by such contact. The mercaptans may either be preferably'used in producing mercaptans by a liquid phase process.

Fig. 2 'diagrammaticallyillustrates the steps employed in producing mercaptans Vin a vapor phase process. 5

As stated hereinabove, the initial step of the processcomprisescontactingapetroleum distillate or vapor containing mercaptans, with an alkaline solution. A solution of caustic soda or a sodium plumbite solution may be used. Although thel 1o reaction -between mercaptans and caustic or plumbite solutions takes place at all concentra- .tions of such solutions, it is desirable that the caustic solution be above 8" B. 'and preferably betw'een about 14 B. and 16 Be. for commer- '15 cial operations. No advantage is attained by employing caustic soda solutions. above about 20 B. Sodium plumbite solutions made up of 14-16 B. caustic soda solution initially saturated with lead oxide, are well Vadaptedfior the 20 purposes of 'this invention.

As shown in Fig. 1, a petroleum oil or distillate containing mer'captans (such as cracked naphtha), may be supplied to a mixing chamber i and mixed therein with a sodium plumbite or 25 doctor solution. From about 1/40 to 3/ 10 parts by volumeof doctor solutionY may be required, this proportion varying with Ithe mercaptan content of the petroleum distillate being treated. The mixing in the chamber i may take place either 30- at atmospheric or superatmospheric temperature. Obviously, ii superatmospheric temperatures are .employed, the mixing device' may be provided high in mercaptans is treated, the lead mercaptides are'precpitated and will exist as solids in the interphase between the oil and the aqueous doctor solution. At lower concentrations and atv high'erc temperatures the mercaptides would be 45 soluble in the aqueous solution. The naphtha, together with its contained higher lead mercapdes, may be removed by decantation and sent to a still 3 wherein separation, between the lead mercaptides and the'naphtha is-accomplished by 50 vaporizing the naphtha, the naphtha Yvapors passing into a condenser I and beingfcollected in a tank 5. A residue of higher lead mercaptides is thus' obtained; these higher lead mercaptides may then be hydrolyzed in the presence. as'

boiled to hydrolyze the mercaptides.

of water, either in the same still 3 or, as shown in Fig. 1, in a separate distillation unit 6. The distillation of the mercaptides with steam decomposes the mercaptides to mercaptans which pass off as a vapor and may be condensed as by condenser 'I and collected in a. suitable receptacle 8. Such digestion or distillation can be carried out at any desired temperature and pressure, but temperatures of from about 150 F. to 300 F. and pressures up to 100 pounds have been successully employed.

'I'he sodium plumbite solution together with its lower mercaptides remaining in the settling tank 2 may be sent to a still 9 and there distilled, the mercaptides being hydrolyzed so as to form mercaptans which pass oi as a vapor and are condensed by suitable condensing means I 0 and then collected in a tank II. The residual sodium plumbitesolution may be recirculated as by line I2 for reuse in the treatment of further batches of naphtha.

In a process of the character described hereinabove, mercaptans of the entire naphtha boiling point range are obtained. If it is merely desired to obtain lower boiling mercaptans, then relatively low boiling point hydrocarbon distillates should'be treated. The higher boiling mercaptans occur inthe higher boiling distillates.

As an illustrative example of the process, a crude cracked distillate produced in the cracking of a California gas oil and containing 0.138 mercaptan sulfur, was treated at room temperature with T16 its volume of 10% caustic soda solution. About 60% of the mercaptans contained in the distillate were removed as sodium mercaptides. The distillate was separated from the vaqueous alkaline solution and the aqueous solution then In the arrangement of apparatus used, the condensate obtained by the distillation nof the caustic soda solution separated into two layers, the upper consisting of substantially pure mercaptans and the lower of water. the still in order to maintain the concentration of the sodium hydroxide in the boiling liquid substantially constant.

The -petroleum distillate separated from the caustic soda solution and its mercaptides, contained substantially no sulfur.

Since the lower molecular weight mercaptans are somewhat soluble in water, it might be desirable to increase the recovery by extracting such dissolved rnercaptans from the watery condensate by means of an organic solvent such as, for example, a purified petroleumdistillate having a boiling point range somewhat different from that of the mercaptans extracted. The petroleum distillate extract may then be redistilled so as to produce substantially. pure mercaptans.

It is to be noted that in a process of the character described hereinabove, when the petroleum distillate has be'en treated 'with a doctor solution so that lead mercaptides are present in the petroleum distillate, such petroleum distillate should be separated from the doctor solution and vaporized, as in the still 3, in the substantial absence of water, so as to prevent the hydrolysis of the mercaptides during the distillation of the naphtha.

Fig. 2 illustrates what we term a vapor phase modication of our process. The hydrocarbon vapors may be admitted into a tower I 5 as by line I6. A caustic soda or doctor solution supplied by line I'I,`passes downwardly through the tower and in counter-current relationship to the va- The water was cycled back to.

pors. The tower is preferably lled with Raschig y rings or other means for extending the contact area.

The hydrocarbon vapors, after being contacted with the alkaline solution, may pass through trap I8 adapted to remove water or alkaline solution therefrom and return it to the tower I5. The puried hydrocarbon vapors are discharged by line I9. The alkaline solution, together with its mercaptides, may be sent to a dige'ster or still 20 wherein it is boiled and the mercaptides converted into mercaptans. The vapors may pass through a reux condenser 2l, the aqueous vapors being returned to the still 20. captans may pass by line 22 through a condenser 23 and be discharged into a tank 24. 'I'he caustic solution from which the mercaptides and mercaptans have been removed, may be returned as by line 25 for use in contacting with additional quantities of hydrocarbon vapors.

A modification applicable to either the liquid phase or vapor phase process comprises the acidication of the spent caustic' soda solution or sodium .plumbite solution and the recovery of mercaptans therefrom as a water-immiscible oil. For example, the caustic soda or sodium plumbite solution, together with its mercaptides, may be diverted as by line 26 into'a vessel 21 and a suitable quantity of mineral acid added thereto as by line 28. 4Any acid may be employedalthough sulfuric and hydrochloric acids may be ordinarily used. The amount of acid added should be sutilcient to neutralize the solution. After agitating the mixture, the acidied solution is permitted to stand, whereupon the mercaptans will separate in the form of an oily layer which can be removed by decantation.

In the vapor phase process described hereinabove, the temperatures at which the hydrocarbon vapors are contacted with an alkaline solution may range from atmospheric to temperatures of about 250 F. The higher temperatures are permissible when pressure is employed. The temperatures should be sufliciently high so as to prevent the petroleum vapors from condensing and should be suiciently low to prevent the vapor pressure of mercaptans from interfering with their removal.

Illustrative of a vapor phase process, the following may be cited:

A gaseous mixture consisting essentially of butane and butenes having a boilingpoint range of between 20 F. and 45 F. and containing 0.39% by weight of sulfur, principally as methyl mercaptans, was scrubbed at atmospheric temperature with a sodium plumbite solution made up of 14 B. caustic soda solution initially saturated with lead oxide. The doctor solution was used at the rate of 1 gallon to 45 pounds of the hydrocarbon gas. The sulfur content of the gas was reduced from 0.39% to 0.012%.

After removal from the treating tower, the spent doctor solution, together with its mercaptides, was boiled and the lead mercaptides decomposed with the vaporization of mercaptans. Of the total sulfur bodies present in the spent doctor solution, 81% were recovered from the condensate in the boiling operation as mercaptans. This condensate was a liquid boiling between about 43 F. and 46 F. and consisted of practically pure methyl mercaptan.

l The effect of increasing the treating temperature in the scrubbing -tower may be appreciated from the fact that a similar butane-butene gas The merwhen. scrubbed with a similar doctor solution at 180 F. had its sulfur content reduced only from 0.44% to .05% by weigh The following is another example ot theprocess:

A crude cracked naphtha fraction boiling between 80 F. and 195 F., containing 0.46% total sulfur of which 0.193% was'present as mercaptan sulfur, was vaporized and the vapors contacted at 205 F. with 16 B. caustic soda solution laturated with lead oxide. eration, the total sulfurof the naphtha fraction .was reduced to 0.29% and the mercaptan sulfur was reduced to 0.034%. The spent doctor solution resulting from this contacting step contained 1.11% sulfur. This doctor solution was distilled with steam and the mercaptides decomposed to mercaptans volatile at the boiling temperature. 64% of the sulfur contained in the doctor solution was recovered in the condensate distilled during boiling as mercaptans, these mercaptans having a boiling point range of between 95 F. and 194 F.

It will be evident to those skilled in the art that a simple and eilective method of producing mercaptans has been provided, the process not only producing mercaptans in a concentrated and purified form, but in additon producing hydrocarbon fractions or vapors which are substantially sulfur-free and which therefore are much more amenable to further petroleum refining operations. As a matter of fact, the remaining hydrocarbon vapors or liquids may be used without subsequent treatment for purposes to which such hydrocarbon vapors or liquids are normally adapted. If it is desired to further subject the hydrocarbons to reiining, the removal of the mercaptans permits a material reduction in the amount of reagents ordinarily employed for such subsequent treatment. v,

The-mercaptide-containing solution or the mercaptan-containing solution obtained after either hydrolyzing or acidifying the mercaptides, may be utilized directly for certain purposes. For example, when it is desired to impart a signal odor be scrubbed with a heated mercaptidelution, the mercaptans rectly 'into the gas.

Although as described hereinabove, the process in general comprises contacting the vapor being thus liberated dior distillate with a caustic soda solution or so- After this contacting op.

above, or the use of steam, may be used or mercaptan-containing sol dium plumbite solution at' or above atmospheric temperature, followed either by a hydrolyzing op'- eration accomplished by boiling the alkaline solution or dlstilling it with steam, or by acidifying the alkaline solution, numerous changes and modifications can be made in the process without departing from the spirit of the invention.

For example, when a sodlumlplumbite solution is used, the precipitated leadv mercaptides may be settled or otherwise removed from the solution and then treated separately for the recovery of mercaptans. Either the acid treating modiiication of the process, described 4hereinin the treatment of such lead mercaptides,

Although certain specinc temperatures, conditions, concentrations and quantities have been specifically set forth, it is to be understood that such temperatures. conditions, concentrations, etc., are merely illustrative and those skilledin the art will appreciate that numerous changes and modifications can be made.

All such changes and modifications as come within the scope of the appended claims are embraced thereby. Y Y

We claim:

1. In a process of producing mercaptans from petroleum hydrocarbons, the steps -of contacting vapors of hydrocarbons `containing mercaptans with a sod'um plumbite solution to form lead mercaptides, separating the hydrocarbon vapors from the plumbite solution and mercaptides contained therein, then hydroiyzing the lead mercaptides with steam to convert the mercaptldes into mercaptans, vaporizing the mercaptans, separately condensing said mercaptans, and recirculating the residual plumbite solution into contact with further quantities of hydrocarbon vapors in cyclic operation :of the process.

A2. In a process of producing mercaptans from petroleum hydrocarbons, the steps of contacting hydrocarbons containing mereaptans with a sodium plumbite solution, separatingthe hydrocarbons from the plumbite. solution and lead mercaptides dissolved and suspended therein, hydrolyzing the lead mercaptides contained in the plumbite solution, vaporizing the produced mercaptans, and separately condensing said mercap- Y tans. 

